Process of coating copper with cellulose acetate lacquer



Patented Feb. 13, 1934 UNITEDTSTATES' PROCESS or COATING (0 0 P P, E a W I 'r H V CELLULOSE ACETATE LACQUER Ernest R. Taylor and Harry I. Davis, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of NewYork No Drawing." Application May'25, 1932 Serial No. 613,551

1 Claim.

This invention relates to a process of coating copper with cellulose acetate lacquer, and to copper articles so coated. One object of ourinvention is to provide a process for coating copper articles with a tenaciously adhering film of cellulose acetate lacquer. Another object is to provide copperarticles with a tenaciously adhering coating of cellulose acetate lacquer.

As cellulose acetate has a high dielectric constant, a method of coating copper with cellulose acetate has been much sought in the electrical industry. It has, however, not hitherto been found possible to secure satisfactory adhesion of cellulose acetate lacquer to copper. When a copper panel, cleaned by the methods commonly employed in preparing metals for coating with nitrocellulose lacquer, is coated with cellulose acetate lacquer the lacquer film loosens easily from the copper when the coated panel is scratched or bent. Even when acidic constituents, such as have been used to improve the adhesion of nitrocellulose to metals, are added to the cellulose acetate lacquer, satisfactory adhesion to copper is not obtained.

We have discovered that if copper is treated with a hot alkali solution, washed and dried, and then coated with cellulose acetate lacquer containing certain acidic components, satisfactory adhesion of the lacquer to the copper is obtained.

While copper sheets which have not been cleaned may be subjected directly to the hot alkali treatment, it is preferable to clean the copper surface before submitting it to the treatment with. hot alkali. The cleaning may be done with any commonly known metal cleaner, but we prefer to use a mixture consisting of approximately 80% water, 10% glycerine, and 10% phosphoric acid. After the copper is cleaned, washed and dried, it is ready for the hot alkali treatment.

The minimum concentration of the alkali solution used in treating the copper depends upon the strength of the alkali. Strong alkalies such as sodium hydroxide and potassium hydroxide may be used in concentrations as low as 1% by weight, although we prefer to use 2% solutions. Weaker alkalies such as sodium carbonate and trisodium phosphate are preferably used in concentrations of not less than 2% by weight. Alkalies of comparatively low solubility, such as calcium and barium hydroxides, are preferably used in saturated solution. Alkali solutions of the concentrations mentioned give good results if the copper is immersed in the boiling solution for one minute. Although we prefer to use boiling solutions, the temperature of the alkaline solution may be allowed to fall as low as 80 C. if the time of immersion is lengthened. In the case of strong'alkalies suchas sodium or potassium hydroxide, the time of immersion may be decreased to approximately 30 seconds if the concentration of the alkali is increased to 4% or more.

Upon removal from the alkaline solution, the copper is immediately washed with water and dried.

The copper is then coated with a cellulose acetate lacquer containing an acidic component. The acidic components which we have found useful are certain acids, phenol, and esters of certain acids which hydrolyze in the lacquer coating to give the free acids. Among the acidic substances which we have found useful for improving the adhesion of cellulose acetate lacquers to copper cleaned with hot alkali are: boric acid, lower alkyl esters of boric acid such as isoamyl borate, oxalic acid, lower alkyl esters of oxalic acid such as butyl oxalate, phosphoric acid, formic acid, lower'alkyl esters of formic acid such as methyl and ethyl formates, adipic acid, hydrogen-lower alkyl esters of adipic acid such as methyl hydrogen adipate, malonic acid, tannic acid, and phenol. The acidic component should not be one which will attack the cellulose acetate, thus causing destruction of the lacquer surface. This may readily be determined by test. The substances mentioned above do not, in the proportions specified have adeleterious effect on the cellulose acetate. The acids mentioned may be used in amounts ranging from 0.10% to 2%, approximately, of the total solids content of the lacquer. The esters mentioned may be used in 9 amounts ranging from 2% to 15%, approximately, of the total solids content of the lacquer.

The following lacquer formula is illustrative of one way in which we may compound a cellulose acetate lacquer containing an acidic component for use in our invention:

It will be understood that the above formula is merely' illustrative and that we may use other solvent mixtures, other plasticizers, and other addition agents, such as gums, pigments, etc., commonly known to those skilled in the art. "-10 150 C. would causethe lacquer to soften or deteriorate and are not desirable. v

While we have referred to copper, we found that our invention can also be successfully applied to the lacquering of alloys containing high percentages of copper, such, for instance, as brass and bronze. The term copper, therefore, above and in the appended claims, is to be construed as defining not only substantially pure copper, but also copper alloys containing high percentages of copper. The invention is of course applicable to any copper article, such as sheeting, wire, etc. i

When a cellulose acetate lacquer was coated on a clean copper surface which had not been subjected to treatment with hot alkali, the force have required to strip the'dried lacquer film from the copper was so slight that it could not be measured. When cellulose acetate lacquers containing our acidic components were coated on copper which had been subjected to our hot alkali treatment, the force required to strip the dried lacquer film from the copper'was in most cases greater than that required to strip a nitrocellulose lacquer film from copper, in some cases even twice as great. Thus it will be observed that we have not only obtained improved adhesion for a cellulose derivative lacquer but have provided a method of lacquering which provides a surface of cellulose acetate with its many accompanying advantages :over cellulose nitrate surfaces, such as non-inflammability, non-deterioration by ultra-violet light, increased dielectric properties, etc.

What we claim as our invention and desire to be secured by Letters Patent of the United States is:

A process of lacquering copper, comprising treating the copper with a hot alkaline solution;

washing, drying, and subsequently coating it with a cellulose acetate lacquer containing phosphoric acid.

' ERNEST R. TAYLOR.

HARRY I. DAVIS.

nus 

